System comprising a screw and a tool therefor

ABSTRACT

System comprising a crew and a tool ( 6 ) therefore, in which the screw head ( 1 ) with a slot ( 2 ), the slot ( 2 ) having a first recess ( 3 ) with an approximately straight-walled cross section, and the tool being provided with an engagement section ( 16 ) that is complementary to the first recess ( 3 ). The slot has a second recess ( 11 ) at the bottom of the first recess ( 3 ), with a smaller diameter than that of the recess ( 3 ), and the tool ( 6 ) is provided with a central point ( 17 ) that complements the second recess ( 11 ). The second recess ( 11 ) has a circular cross section and the central point ( 17 ) has a circular cross section.

The present invention relates to a system comprising a screw and a tool;a screw constituting part of the system and a tool constituting part ofthe system.

Screws are known to feature a number of differently shaped slots. Theoldest screw slot is a straight slot that extends diametrically acrossthe screw head. In order to screw such a screw, use is made of ascrewdriver that has a flat front with a straight front edge.

The straight slot has several well-known disadvantages. Therefore, newscrew slots have been developed with a view to avoiding thesedisadvantages. Among these are the cross-slots, which mainly appear asPhilips® slots and Pozidrive® slots.

At the end of the 1960s, the Torx® slot appeared. This has beendescribed in detail in NO 128968. In the axial direction, this screwslot has the general shape of a star with six points, where the pointsare slightly rounded. The walls of the slot that extend down into thescrew head are straight. The tool has been designed to be complementaryto the slot. The Torx® slot remedies many of the disadvantages that areassociated with for instance cross-slots. For all that, the Torx® slotstill has some serious disadvantages. Since the walls are straight, theslot depth will be limited, particularly in conical screw heads, orso-called countersunk heads. If the depth becomes too great, the wallsof the screw head will become very thin at the bottom of the slot, andthe screw head may easily break off in this area.

Due to the depth limitation, the engagement between the tool and theslot will not be very good, and the tool may wobble as the screw isscrewed in or out. The limited engagement between the tool and the screwalso causes the screw to hang badly off the tool when the tool and thescrew are held approximately horizontally. For craftsmen who have toscrew a great number of screws, it is of great importance that the screwhangs on the tool until the screw has caught in the material into whichit is being screwed. As the tool wears, its ability to retain the screwwill worsen.

EP 1039151 shows a TORX-screw with corresponding tool. The screw has anordinary TORX slot and a circular recess below this. This recess has thesame diameter as the internal diameter of the TORX slot. The recess isvery shallow. Even though it is said to prevent the screw from fallingoff the tool, this shallow recess has in fact very little effect. Thescrew shown has a cylindrical head. If the head was conical, the depthof the recess would have to be further reduced or the depth of the slotwould have to be reduced. In any case it would be difficult to make therecess any deeper than shown, since the diameter is so large.

U.S. Pat. No. 6,017,177 shows a screw with a TORX slot; severalembodiments are shown. However, the TORX slot is situated at the bottomof a cavity. Below the TORX slot there is a recess. If the screw headhad been conical very little room had been left for the recess.Consequently, this type of screw is limited to cylindrical heads only.

Often, magnetic screw bit holders are used in order to get the screw tosit/hang better on the tool (the bit). However, the bit may easily rideout of the slot if the direction at which the tool is kept deviates fromthe axial direction of the screw. The depth of the slot is small, andthe bit and the slot have opposing tolerance limits within the standardof tolerance. Besides, not all screws are made of magnetic materials.

Several attempts have been made at designing screw slots that alleviatethe above-mentioned problem.

A screw that features a slot with a polygonal cross section has beendescribed in GB 2329947. One embodiment shows a screw slot made up ofthree steps down into the screw head. The top step has the greatestcross sectional area, the next step a slightly smaller cross sectionalarea, and the lowest step has the smallest cross sectional area. All thesteps have a polygonal cross section. The tool for operating this screwincorporates steps with different cross sectional areas, each stepcomplementing a step in the cross section of the slot.

A screw featuring a slot that, in principle, is identical to theabove-mentioned slot has been described in GB 1150382. However, thisslot consists of only two steps.

The above-mentioned screw slots have a number of serious disadvantages.As all the steps have been designed to transmit torsion, even a minorinaccuracy in the slot will result in a mismatch between the tool andone of the steps, thus making it difficult or impossible to insert thetool into the slot. Even if the tool fits in the slot, it may still bedifficult to insert. The tool must be aligned very carefully with thescrew slot, which obviously results in loss of time.

The screw slot is of a complex design that may entail an increase inmanufacturing costs. However, these manufacturing costs will still beminor compared with the cost of producing a tool as complex as thatwhich is shown in the two above-mentioned publications. The cost of thetool is therefore unduly high.

EP 1039151 screw with corresponding tool. The screw has an ordinary TORXslot and a circular recess below this. This recess has the same diameteras the internal diameter of the TORX slot. The recess is very shallow.Even though it is said to prevent the screw from falling off the tool,this shallow recess have in fact very little effect. The screw shown hasa cylindrical head. If the head was conical, the depth of the recesswould have to be further reduced or the depth of the slot would have tobe reduced. In any case it would be difficult to make the recess anydeeper than shown, since the diameter is so large.

U.S. Pat No. 6,017,177 with a TORX slot several embodiments are shown.However, the TORX slot is situated at the bottom of a cavity. Below theTORX slot there is a recess. If the screw head had been conical verylittle room had been left for the recess. Consequently, this type ofscrew is limited to cylindrical heads only.

DE 4413782 shows a screw with a first, tapered step for transmission oftorsion, the top of which has a circular or hexagonal cross section, andthe bottom of which has a hexagonal cross section. Below this is asecond, hexagonal step with straight walls.

In addition to the fact that this system has several of thedisadvantages that characterise the first two mentioned screw slots,such as the complexity and cost of the tools, the screw slot accordingto DE 4413782 has a further, considerable disadvantage. If, duringoperation, the tool is pulled fractionally away from the screw in theaxial direction, the tool will disengage from the first tapered step. Byso doing, all torsion will be transmitted through the second step alone.This step has a significantly smaller diameter than the first step, andthe strain on the tool and the screw increases considerably. Thus, thereis a risk of destroying the tool or “rounding” the hole.

EP 257664 shows a cross-slotted screw head in which the upper step is aconventional cross-slot and the lower step is a polygon with straightwalls. Both a conventional screwdriver for a cross-slotted screw and aspecially adapted screwdriver may be used with this. This slot also hasmany of the above-mentioned disadvantages. The specially adaptedscrewdriver is complex and costly to produce. It also has thatdisadvantage which is common to all generally conical slots, which isthat the screwdriver is inclined to move away from the screw in theaxial direction. If this happens, the area of contact is reduced, andthe strain on the slot and the screwdriver will increase. In particular,the strain on the lower, smaller diameter step will increase, and thetool or the screw may easily be damaged in this area.

The object of the present invention is to provide a system consisting ofa slotted screw and a tool, in which good contact is established betweenthe screw and the tool, so as to enable the screw to be held on the toolwithout falling, off, and in which good contact between the screw slotand the tool is achieved without the risk of a small axial movement ofthe tool away from the screw significantly increasing the risk of damageto the slot or the tool; in which is achieved a tool that is easy toproduce and which does not entail significant cost increases, and inwhich it is possible to use a conventional, standard tool in a screwslot according to the present invention with the same effect as if itwere used in a conventional, standard screw slot.

It is also an object of the present invention to achieve theabove-mentioned object without weakening the walls of a conical screwhead.

The invention will now be described by way of an example of anembodiment, with reference to the accompanying figures, in which:

FIG. 1 shows a section through a front part of a tool according to thepresent invention,

FIG. 2 shows a section through a screw head with a slot according to thepresent invention, in which has been placed a tool according to thepresent invention, and

FIG. 3 is a plan view of a screw head with a slot according to thepresent invention.

The example of an embodiment shows a screw head with a Torx® slot.However, the invention is not limited to this type of slot, and mayeasily be adapted to other types of slots that feature substantiallystraight walls. A plan view of a screw head 1 with a Torx® slot 2 isshown in FIG. 3. The slot 2 is a recess 3 in the screw head, shaped as astar with six points, and consisting of rounded points 4 that extendoutwards from an imaginary circle 2. Depending on the direction ofrotation, a tool 6 (see FIGS. 1 and 2) will engage contacting surfaces 7and 8 on one side or the other of each point 4.

FIG. 2 shows a section through screw head 1. The recess 3, the walls 9of which are approximately straight, extends down into the screw head 1.The cross section of the recess 3 retains the shape of a star with sixpoints throughout the straight-walled part. The depth of the recess 3 islimited by the minimum allowable wall thickness 10 at the bottom of therecess 3.

The screw slot 2 according to the present invention comprises a further,central recess 11 at the bottom of the six-pointed recess 3. Thiscentral recess 11 has a circular cross section and a significantlysmaller diameter than recess 3. The walls 12 of the central recess 11may be approximately straight, but are preferably slightly inclined sothat the bottom 13 of the recess 11 has a diameter that is slightlysmaller than that of the upper part 14 of the recess 11.

A downward sloping transition surface 15 is formed between the upperpart 14 of the central recess 11 and the walls 9 of the six-pointedrecess 3.

The tool 6 has an engagement section 16 that is designed to engage therecess 3. The shape of the engagement section 16 complements the shapeof the recess 3, but has a slightly smaller diameter than the recess 3,so as to allow it to be inserted into the recess 3 without difficulties,in the same manner as for existing tool-slot combinations.

The tool also has a central point 17 with a circular cross section. Thediameter of the centre point 17 is slightly smaller than that of thecentral recess 11. A surface 18 extends from the central point 17 to theengagement section 16. The angle of inclination of the surface 18 issmaller than that of the transition surface 15. Thus, a space 19 isformed between the surfaces 15 and 18 when a tool 6 is inserted into theslot 2. The space 19 diverges towards the central point 17. This ensuresthat the tool engages the walls 9 of the recess 3 across the entireheight of the recess 3, thereby ensuring maximum engagement between theengagement section 16 of the tool and the recess 3.

Furthermore, in the case of screws that have undergone surfacetreatment, the diverging space 19 allows any excess coating to collectin the space 19 without obstructing the engagement between the tool andthe slot. If no space 19 had been provided, coating residue would settleon the surface 15 and at the bottom 13 of the recess 11, and therebyprevent sufficient engagement between the tool 6 and the screw slot 2.

The central point 17 and the recess 11 ensure longer-lasting, efficientengagement between the tool 6 and the slot, and allows the screw toremain on the tool without falling off, through friction. The angularmovement (wobbling) between the tool and the screw is also reducedconsiderably.

The central point 17 may, as shown, have a length than is shorter thanthe height of the recess 3, so as to enable the engagement section 16 ofthe tool 6 to engage the recess 3 before the central point 17 engagesthe recess 11. The tool may however also have a central point 17 that islonger than the height of the recess 3, so as to enable the centralpoint 17 to engage the recess 11 before the engagement section 16engages the recess 3. This facilitates the insertion of the tool intothe slot, as the central point 17 is inserted into the recess 3,possibly hits the sloping transition surface 15, and slides into therecess 11. Thus, the tool need only be rotated about the central point17 in order to bring the engagement section 16 into alignment with therecess 3.

The screw slot does not preclude the use of a conventional tool withouta central point 17, but the advantages afforded by the central point 17and the recess 11 will not be obtained. As such, screws featuring a slotaccording to the present invention may be produced without consideringthe types of tool available to craftsmen and others, as the recess 3 isof a conventional design, e.g. the Torx® type.

A craftsman wishing to make use of the advantages of the slot may simplypurchase a tool according to the present invention at a later date.

1. System comprising a screw and a tool therefore, in which the screw has a screw head with a top surface and a slot, the slot having a first recess adjoining the top surface, the slot having an approximately straight-walled cross section, and the tool is provided with an engagement section that is complementary to the first recess, and where the slot has a second recess at a bottom of the first recess, with a smaller diameter than that of the first recess, and the tool is provided with a central point that complements the second recess, the first recess is shaped as a hexalobular star with six points viewed in an axial direction of the screw, the second recess has a circular cross section, and the central point of the tool has a circular cross section, wherein the screw comprises a transition surface between the first and second recesses, which extends to the second recess at a first angle, and the tool comprises a surface between the engagement section and the central point, which extends to the central point at a second angle, the first angle being steeper than the second angle, so that a space is formed between the transition surface and the surface when the tool is inserted into the slot, the space diverging towards the central point.
 2. System according to claim 1, wherein the diameter of the second recess is substantially smaller than the diameter of the first recess.
 3. System according to claim 1, wherein the first recess and the second recess have substantially the same depth. 